This in vitro study sought to assess the effect of repetitive PBMT on the viability of fibroblasts following aPDT with indocyanine green (ICG). In this in vitro experimental study, human gingival fibroblasts (HGFs) were obtained and incubated in a culture medium. After reaching 10 000 cells cm À2 , the cells were divided into five groups of control, aPDT with ICG and 808 nm (energy density of 24 J cm À2 ), PBMT immediately after aPDT, PBMT with 660 nm (energy density of 7.2 J cm À2 ) immediately and 24 h after aPDT and PBMT immediately and 24 and 48 h after aPDT in 48-well plates. Cell viability was evaluated using the methyl thiazolyl tetrazolium (MTT) assay after 1, 4 and 7 days of incubation. Statistical analyses were performed using one-way ANOVA. Cell viability significantly decreased in group 2 (P < 0.002). We observed no significant increase in cell viability at any time point in group 3 (P > 0.05). Cell viability significantly increased in groups 4 and 5 after the first day of incubation (P < 0.000). Emission of 660 nm as PBMT for two and three times along with passage of time would increase the viability of HGFs following aPDT with ICG.